NASA's High Energy Solar Spectroscopic Imager spacecraft --
an international mission to explore the basic physics of particle
acceleration and energy release in solar flares -- has sustained
substantial damage during vibration testing. Repairs to the
spacecraft, known as HESSI, will likely delay its launch to no
earlier than January 2001.

The damage was caused when a test device that simulates
vibrations the spacecraft can expect during launch delivered
approximately 20G's, ten times the appropriate levels for the
test. As a result, the spacecraft's structure was damaged and two
of the four solar arrays were cracked. The status of the HESSI
instrument is not currently known.

Engineers are optimistic that the structure, instrument boxes
and detectors were not harmed, but further analysis will be
required to determine the full extent of the damage. Both damaged
solar arrays need to be replaced.

The incident occurred March 21 while the spacecraft was
undergoing vibration testing in facilities at NASA's Jet
Propulsion Laboratory, Pasadena, CA.

The spacecraft and vibration facility are impounded pending
an independent failure review board that will be chaired by NASA's
Marshall Space Flight Center, Huntsville, AL, and supported with
experts from NASA's Goddard Space Flight Center, Greenbelt, MD;
NASA Headquarters, Washington, DC; and other NASA centers as
required. This board will begin investigating in the next several
days, and is expected to conclude its efforts in six to eight
weeks.

Following its release from the vibration facility, the HESSI
team will disassemble the spacecraft, re-inspect it, and perform
needed repairs. It is expected replacement of the solar arrays
will take four to six months.

HESSI was scheduled to be launched on a Pegasus rocket in July
2000. While a new launch date is not known, current estimates,
depending on the amount of work that will have to be done, put a
launch no earlier than January 2001. The cost to repair the
satellite, which will determine how long the mission will be
delayed, has not yet been determined. NASA's cost for the HESSI
spacecraft was budgeted at $40 million. Development, launch
vehicle and mission operations costs bring the total mission value
to $75 million.

HESSI is a Small Explorer mission and is managed by Goddard
under the Explorer Program. The science team includes co-
investigators from Switzerland, Scotland, Japan, France and The
Netherlands.

More information on the HESSI mission can be found on the
Internet at: